Textures in Polygonal Arrangements of Square Nanoparticles in Nematic Liquid Crystal Matrices

• Published in: Langmuir Vol. 27; no. 21; pp. 13335 - 13341
• Main Authors: Phillips, Paul M, Mei, N, Soulé, Ezequiel R, Reven, Linda, Rey, Alejandro D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.11.2011
• Subjects: Absorption; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Liquid Crystals - chemistry; Materials: Nano-and Mesostructured Materials, Polymers, Gels, Liquid Crystals, Composites; Nanoparticles - chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Surface charge; Confinement; Nanoparticle; Equation; High temperature; Orientation; Liquid crystals; Modeling; Texture; Design; Particle; Thermodynamics; Energy; Ordering; Defect; Models; Nanocomposite; Anchoring
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la203226g

A systematic analysis of defect textures in faceted nanoparticles with polygonal configurations embedded in a nematic matrix is performed using the Landau–de Gennes model, homeotropic strong anchoring in a square domain with uniform alignment in the outer boundaries. Defect and textures are analyzed as functions of temperature T, polygon size R, and polygon number N. For nematic nanocomposites, the texture satisfies a defect charge balance equation between bulk and surface (particle corner) charges. Upon decreasing the temperature, the central bulk defects split and together with other −1/2 bulk defects are absorbed by the nanoparticle’s corners. Increasing the lattice size decreases confinement and eliminates bulk defects. Increasing the polygon number increases the central defect charge at high temperature and the number of surface defects at lower temperatures. The excess energy per particle is lower in even than in odd polygons, and it is minimized for a square particle arrangement. These discrete modeling results show for first time that, even under strong anchoring, defects are attached to particles as corner defects, leaving behind a low energy homogeneous orientation field that favors nanoparticle ordering in nematic matrices. These new insights are consistent with recent thermodynamic approaches to nematic nanocomposites that predict the existence of novel nematic/crystal phases and can be used to design nanocomposites with orientational and positional order.